In an optical communications system that uses one or more optical fibers, wherein an optical coupler having a light sending side and a light receiving side is used, there has been a need for an optical coupling system wherein a divergent light beam that is emitted from the light sending side of the optical coupler is collected and formed into a convergent light beam that is then incident onto an end surface of an optical fiber on the light receiving side of the optical coupler.
Conventionally, a so-called ball lens (i.e., a spherical lens) has been used as a lens in such an optical coupling system to collect the light and to form the light into a convergent beam. Such a lens has an advantage in that, since no alignment is required due to its spherical shape, it is easily mounted. However, there is a problem in that a ball lens does not efficiently condense light due to the spherical aberration of such a lens being large.
In Japanese Laid-Open Patent Application No. H09-061665 another design is disclosed that uses an aspherical lens as a coupling lens in an optical communications system that enables the light to be more efficiently condensed, as compared with using a ball lens, and thus the coupling efficiency of the optical coupler is enhanced.
With a lens having a fixed optical axis such as with an aspherical lens, it is generally difficult to obtain a desired optical performance unless the alignment of the lens is accurately performed. When the lens is used as a component of an optical coupler in an optical communications system, alignment errors (especially, inclination errors) of the lens result in a large shifting of the position of the focus point, and thus the coupling efficiency of the optical coupler may be remarkably reduced.
Conventionally, a lens of an optical coupler in an optical communications system must be accurately aligned with meticulous care, due to the mounting operation of the lens being less than ‘user friendly’.